The present disclosure is directed to a testing device. It is a device especially to be used for testing the bond between fibers and supportive polymer bodies surrounding the fibers. A typical device made of composite materials is a fly rod. Fibers are arranged parallel to one another and are bonded together into a composite body by placing a resin polymer matrix around the fibers. The fibers and resin are shaped to the final shape. The fibers can be made of many materials. For instance, fiber glass is a popular fiber. It is relatively large in comparison with carbon fibers. Carbon fibers are relatively small, one of the smallest fiber of commercial interest. The measurements for the fibers may vary but it is not uncommon for fibers in composite materials to be in the range from about 5 to about 250 microns diameter. The quality of the composite article of manufacture is in part determined by the bond between individual fibers and the surrounding matrix. This bond is the location at which failure may occur. In fact, the grip between the matrix and the fiber in the matrix is an important factor in providing a high quality article of manufacture utilizing composite materials.
One mode of testing such a device is to attempt to push or pull the fiber to determine breaking of the bond between the fiber and the supportive matrix. With fibers as small as 5 microns diameter, this is extremely difficult to do. Moreover, because there are so many fibers in a typical manufactured article, it is essential to test many fibers. Going back to the example of a fly rod and utilizing graphite fibers having a typical diameter of about 5 or 6 microns, the cross section of the fly rod even at the narrow tip areas may well include over 100,000 fibers. It would not be uncommon to have as many as one million fibers arranged more or less parallel to one another structurally supporting a composite article of manufacture. For this reason, it is important to test many fibers. This provides a statistical data base which enables compiling of meaningful data as opposed to data regarding the bond between a single fiber and the surrounding matrix.
The apparatus of this disclosure is a system enabling testing of individual fibers. Across a cast body made of composite materials (that term shall be applied hereinafter to a set of parallel fibers adhesively held together with a surrounding cured matrix), a transverse cut is made to define an exposed face. This exposed face is ideally perpendicular to the fibers. At least, the bulk of the fibers should be approximately perpendicular to the face. The face is preferably mechanically polished and smoothed so that the cut ends of the various fibers intersected by the face maintain their nominal size and shape. A stylus featuring a small tip or point is pressed against the end of a fiber. While it is easy to describe this in general terms, there is a great deal of difficulty because the stylus is far larger than a single fiber and the point of contact of a particular stylus against the face (intersecting 100,000 or more fibers) is difficult to ascertain. The data proves nothing if the point of the stylus strikes against the matrix. Moreover, it does not really prove much if the point of the stylus contacts a fiber at the edge of the fiber, meaning the interface between fiber and matrix. Rather, the ideal approach is that the tip of the stylus contact the fiber at the center of the fiber. It is rather difficult to line up a large stylus and position the tip of the stylus at the precise center of a fiber which is only 5 or 6 microns in diameter.
The present apparatus approaches this problem by arranging an optical microscope system which looks at the sample supported on a stage in the microscope system which is movable in x, y and z dimensions. Optical system microscopes able to properly focus on and provide an image of the tips of fibers measuring only 5 microns in diameter are available. Such an optical system, of course, requires a fairly large lense system, extremely large in contrast with the diameter of the fiber undergoing testing. In fact, it can be reasonably said that the lense is perhaps thousands of times greater in diameter than the fiber which is being viewed through the lense. Moreover, the lense must be arranged parallel to the face of the specimen so that it can view the end of the fiber. At this juncture, it must not only be parallel but relatively close. This precludes inserting any kind of instrument in the gap between the lense and the test specimen. Even if an instrument could be inserted in that region, it would so obscure the optical view that one could not know precisely where the instrument was located, at least with the accuracy sufficient to land the tip of the inserted instrument precisely at the center of an optical fiber. Restated, this simply recognizes the fact that the test instrument (a pointed stylus) is so large that its insertion would obscure the optical system whereby the instrument tip is located. If the tip cannot be located, there is no certainty that it contacts the matrix or fiber; it simply will contact something at some location on the face. Even that is not sufficient by hindsight inspection looking for the dimple or indention formed by the previous use of a pointed instrument. The reason that post testing inspection is not possible is that the instrument may contact the face to form an indention of perhaps 1 or 2 microns diameter which is simply too small to be located by post dimpling inspection.
The present apparatus suggests a system for overcoming these and other handicaps. The system utilizes an optical microscope system so that an observer can view the cut specimen through the optical system. The field of view is perpendicular to the face of the specimen. Through the use of conventional optical cross hairs, a particular point in the target area can be located. The stage can be adjusted in position to obtain a sharp focus and also to locate the cross hair intersection over a particular fiber. Once this has been accomplished, a particular fiber being designated, the next step in use of the apparatus is then to position the stylus at the location at the cross hair. The stylus, having a shaped tip thereon, is then moved into the location where the cross hair intersection once was located. To this end, the optical axis through the microscope system defines what might be termed a reference axis. This reference axis is used as a means of determing an origin in an x-y system. The optical system thus defines the origin or the point of 0,0. Off to the side at some measure known by x and y coordinates, a parallel positioned stylus is located. The distance between the axis of the stylus and the optical system is a specific measure. This measurement can be determined to an accuracy of less than one micron in x and y dimensions. In this arrangement, the stylus is made parallel to the optical axis. It is offset by a specific distance. This distance will be represented hereinafter as the measurements of m and n which are offsets measured in microns from the origin of the x-y plane and which is coincident with the optical axis. The values of m and n are fixed on manufacture of the apparatus. Thus, a particular stylus is installed and mounted so that it is parallel to the axis through the origin. The tip is located at a distance known by m and n from the origin. These measurements are determined in microns in the preferred embodiment. This offset (m and n) is stored in memory for subsequent translation. The tip of the stylus is located at a vertical location or z position. This tip is located so that it is several thousand microns above the face of the specimen when the specimen is viewed optically. That is, the lense system is placed a specified height above the sample so that a proper focus can be determined. This positions the tip in space several thousand microns above the face of the specimen. At the time that a test is undertaken, the tip is first moved to the previously established cross hair location by adjustment of the x-y stage through the distances of m and n. Once this is accomplished, the tip of the stylus is then lined up with the particular cross hair location previously observed visually. At that juncture, using movement along the z axis, the tip of the stylus is brought in contact with the specimen with the assurance that it strikes the specimen at a predetermined location. After testing in a fashion to be described, the indention at that particular cross hair location can then be inspected visually to be sure that the test has been completed. Moreover, the break in the bond, if any, can be visually inspected to make qualitative determinations regarding the bond holding the components of the composite material together.
The present apparatus is therefore summarized as an optical system which has an optical eye piece to be viewed while supporting an objective lens positioned above a sample holder. The sample holder is supported on an x-y-z stage which is driven by x-y-z stepping motors connected to appropriate gear drive systems. Conveniently, the optical system also includes a video camera and a mounting for a still camera. The optical lense system defines an optical axis or an origin on x, y coordinates at 0,0. An offset stylus is located at a distance of m and n from the origin at 0,0. This measure if fixed at the time of manufacture and installation of the particular stylus. The offset measurements of m and n are stored in memory. The memory controls a drive signal for stepping motor drivers. When the motors are driven, thereby traversing the stylus tip to the point coincident with the optical axis or the origin at 0,0, and a test can be made. The device also includes means for traversing in the z direction. A load cell measures loading, and travel in the z direction is also measured, thereby enabling a measurement of a stylus tip penetration into the composite material. The stylus tip enters at the specified location determined by optical inspection and aligned with the cross hair in the optical system.